Hi Kim,
That is a great question! I am sure you will get plenty of feedback from the contractors around here and other investors that have good contractors that they work with.
I have been working with contractors for over 12 years as a Designer, Estimator, and a Supplier of all things interior and a few things exterior.
First is to have realistic expectations-find out what is standard in your area for timelines and pricing (each season is different for different contractors) Interior contractors (flooring, drywall, paint, cabinets, etc are quite busy from June-Aug and October-January in our area as weather forces projects to move inside and after the spring build rush). Ask around regarding labor rates and how far out they are typically booked. If many contractors in your area are booked 3-4 weeks out, then tell them what your closing date will be on a property and get them penciled in, or be prepared to wait. Being pro-active will go a long way. Don't schedule them then cancel less than a week before the project...that is food off their table.
Clear Communication - don't assume anything. Have a detailed and clear scope of work. Until you work with a contractor long enough that you both know what to expect - more info is always better than less. Ask for input from the experts. Ask them what you are forgetting, or what other contractors will be involved in each portion of a project. My favorite question is, "what is NOT included that I need to be thinking about?". Who else will I need to complete this "Kitchen remodel", Tub replacement, Flooring installation?
Often, they want you to know what you want - or what you want to accomplish - but they don't want to give design advice. This is a generalization, but most contractors that I have worked with just want to go in and do the job and get on to the next one.
Work around their schedule - early morning, lunch breaks and after the end of the day are the best time for contractors to meet onsite for bidding and walk-through s. Tell them in advance the general size of the project so they can be prepared. If you are going to be doing multiple walk thru s while you look at properties then offer to pay for their time to be onsite (flat fee).
As with most of us, don't waste their time. Be respectful of their expertise. Be prepared.
And...I would not be the Designer or Sales Manager if I didn't say - the company I have my day job with works in Sweet Home and I would love to chat with you more!